1. Technical Field
This invention relates to a controlled steel composition useful as a powder that is plasma sprayable and functions as a heat transferring solid lubricant when deposited as a thin coating on surfaces exposed to high temperatures.
2. Discussion of the Prior Art
Automotive engines present a wide variety of interengaging components that generate friction as a result of interengagement. For example, sliding contact between pistons or piston rings with the cylinder bore walls of an internal combustion engine, account for a significant portion of total engine friction. It is desirable to significantly reduce such friction, by use of durable anti-friction coatings, particularly on the cylinder bore walls, to thereby improve engine efficiency and fuel economy, while allowing heat to be transmitted across such coatings to facilitate the operation of the engine cooling system.
Nickel plating on pistons and cylinder bore walls has been used for some time to provide corrosion resistance to iron substrates while offering only limited reduction of friction because of the softness and inadequate formation of nickel oxide (see U.S. Pat. No. 991,404). Chromium or chromium oxide coatings have been selectively used in the 1980's to enhance wear resistance of engine surfaces, but such coatings are difficult to apply, are unstable, very costly, and fail to significantly reduce friction because of their lack of holding an oil film, have high hardness, and often are incompatible with piston ring materials. In the same time period, iron and molybdenum powders also have been jointly applied to aluminum cylinder bore walls in very thin films to promote abrasion resistance. Such system offers only a limited advantage. Molybdenum particles and the many oxide forms of iron that result from the conventional application processes, do not possess a low coefficient of friction that will allow for appreciable gains in engine efficiency and fuel economy.